A group of mutants of S. avium and L. casei have been generated that are blocked at each step of pentitol metabolism. These mutants are being used to define and describe the components of the pentitol dissimilating system found in these two microorganisms. Thus the highly specialized soluble component of the xylitol PEP-phosphotransferase system (PTS), namely Enzyme III, is being purified to homogeneity prior to its complete characterization. Similarly, the NAD-specific xylitol-5-P dehydrogenase is also being purified and characterized biochemically. In addition, these mutants are also being used to determine which intermediate products of pentitol metabolism are responsible for inducing the xylitol specific components of the PTS and the dehydrogenase. Cytophaga species isolated from subgingival plaque of patients with periodontitis have been characterized biochemically and shown to be facultative aerobes capable of inducing a functional tricatboxylic acid cycle. The organisms appear to be incapable of producing either gingivitis or bone loss when implanted in germ-free animal models. They have been shown to coaggregate with Actinomyces israeli, another inhabitant of the periodontal pocket.